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TIMER1 with 32khz osc doesnt work

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PCM programmer

Joined: 06 Sep 2003
Posts: 21708

Posted: Fri Feb 23, 2007 5:54 pm

I ran your program (shown below) on a PicDem2-Plus and I got this:

Quote:

61622
63899
63899
63899
63899
63899
63900
63900
63900
63899

Code:

#include <16F877A.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

void main(void)
{
int16 k;
int8 i;

for(i = 0; i < 10; i++)
{
setup_timer_1(T1_DISABLED);
set_timer1(32768);
setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1|T1_CLK_OUT);
delay_ms(950);
setup_timer_1(T1_DISABLED);
k = get_timer1();
printf("%lu\n\r", k);
}

}

Imanjl

Joined: 15 Nov 2004
Posts: 42

Posted: Sat Feb 24, 2007 2:59 am

rnielsen wrote:

If you need accurate timing then you will need to allow the timer to roll over, causing an interrupt, and have that flag whatever you want done.

I wrote a new program without using get_timer1(); at this time when timer overflows(1s) it generates an interrupt .but still 1 second isnt accurate . This program generates 1 second in about 850-950mS .

Code:

#int_TIMER1
TIMER1_isr(){
set_timer1(32768);
count++;}

void main(void)
{int16 k;
int8 i;
setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1|T1_CLK_OUT);
set_timer1(32766);

loop:
...
...
printf("\ntimer1=%lu\n\r",count);
...
goto loop ;}

hi pcm programmer ,ur result shows that the program works fine on Picdem2 cause (63900-32768)*30.5us=949ms .Maybe there is something wrong with my hardware according to microchip refrence manual,32.768 need two 33pf capacitors I use 30pf for c1 and c2 but I dont think it affects the result so much ,whats the Picdem2 caps value for timer1 ?

Besides the pic is on the bread board :

Quote:

Design Tips
2. You should ensure the your layout uses good PCB layout techniques so that noise does not couple onto the Timer1 oscillator lines.

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